ELECTROLYTIC ANALYSIS OF METALS
washed and, what is of great practical importance, allow of the electrolysis
of solutions varying in volume from 100 to 300-400 c.c. and of electrolysis
in presence of precipitates. The cathode consists of an open cylinder 5 cm.
high and 3-5 cm. in diameter, formed of iridised
platinum gauze and supported by a thick plati-
num wire (Fig. ig,a). The anode forms a plati-
num wire spiral (Fig. 19, b).
In many cases, especially when copper and
lead are being determined simultaneously, the
Winkler spiral may be replaced with advantage
by a small cylinder of iridised, matte platinum
gauze,1 1-5 cm. in diameter and 5 cm. high (Fig.
19, c] ; on this as much as 0-3 gram of lead may
be conveniently deposited as peroxide, whilst
the copper is deposited on the cathode.
Supports. The most convenient and the
most common are those of Classen. They con-
sist of a heavy iron foot carrying a thick vertical
glass rod. To the insulating rod are fixed by
means of pressure screws, the electrode holders,
those for Classen electrodes being a ring furnished with three platinum
points on which the dish rests and a binding screw for suspending the
anode, and those for Winkler electrodes two connecting screws (see Fig.
(b) WITH ROTATING ELEC-
TRODES. Electrodes. These may
be : the Classen dish, within which
the disc acting as anode revolves;
or the Winkler cathode, inside
which rotates a platinum spiral
wound round a glass rod to give it
solidity (Fig. 21). Other electrodes
which are much in use and very
convenient are those of Fischer,
consisting of two concentric gauze
cylinders (Fig. 20, a, b), insulated
by quartz rods ; the electrodes re-
main stationary, the liquid being
kept in motion by a glass stirrer
(Fig. 20, c) revolving inside the
Stands. These, besides supporting
the electrodes, should permit of the
rotation of one of the electrodes or of a stirrer. In its simplest form, a
stand for rotating electrodes is shown in Fig. 21. One of the screws of
the stand is replaced by a support carrying a rotating axis on which the
1 Belasio : "Analysis of Bronzes for Ornamentation, so-called Nickel Bronzes" [Ras-
segna mineraria, 1909, XXXI, p. 50).
weigh little (14-15 grams), permit perfect mixing of the liquid, are readily